1. Field of the Invention
The subject invention relates to a target assembly for use with a laser apparatus and a control or readout apparatus for assessing the alignment of a sheave or for properly aligning a height gage.
2. Description of the Related Art
Many prior art machines include parts that are movable relative to one another. Optimum efficiency of the machines can be achieved when the movable parts are properly aligned relative to one another. However, use of the prior art machines invariably results in the respective movable parts becoming misaligned relative to one another.
The prior art also includes assemblies with parts that must be positioned at a specified location relative to a fixed frame of reference.
The prior art includes many types of apparatus for assessing the alignment of two parts relative to one another. These prior art alignment devices include mechanical devices, such as levels, optical devices, such as sight gages, and electrical devices.
The assignee of the subject invention has developed several alignment systems that employ at least one laser emitter, at least one light-sensitive target cell, a control system and/or readout device. The prior art laser emitter projects a substantially straight laser beam toward the light-sensitive target cell. The prior art target cell identifies the location of the center of energy of the laser beam that impinges on the target cell. The target cell generates signals that can be analyzed by the control system to assess the relative position of the target relative to the laser and to assess the alignment of the laser beam impinging on the target. The data developed in this manner can be used to adjust the position and/or alignment of one or the other of the components being aligned.
The prior art systems of laser emitters and targets have been used very successfully to align parts relative to a specified central axis. For example, a prior art laser alignment system has been used to align rotors and stators along the rotational axis of a turbine. Another prior art laser alignment system has been used to align a rotating tool, such as a drill, to a work piece upon which the tool will act. An example of a prior art laser en alignment system for projecting a rotational axis is shown in the assignee""s U.S. Pat. No. 4,566,202.
The assignee of the subject invention also has developed an apparatus for sweeping at least one laser plane. This prior art apparatus works by directing a laser beam into a penta-prism that reflects an input laser beam internally and produces an output beam that is aligned precisely at right angles to the input beam. The penta-prism then is rotated about the axis of the input beam. As a result, the output beam sweeps an laser plane that is perpendicular to the input beam. Targets can be mounted on objects at locations remote from the laser emitter. The positions of these targets and the objects to which the targets are mounted then can be determined precisely by signals generated as the laser beam sweeps across the targets. An apparatus that sweeps such a flat laser plane is disclosed in the assignee""s earlier U.S. Pat. No. 4,468,119. An apparatus capable of sweeping a plurality of mutually perpendicular planes is disclosed in the assignee""s U.S. Pat. No. 5,307,368. The assignee""s U.S. Pat. No. 5,929,984 discloses a system for generating at least one laser scan plane and laser beams that are perpendicular to the plane. The system disclosed in the assignee""s U.S. Pat. No. 5,929,984 can be used, for example, to properly position components of an airplane during the manufacture of the airplane.
A sheave is an apparatus that has at least two grooved disks or wheels that rotate about parallel axes. Sheaves also are referred to as pulleys. Sheave systems are incorporated into many industrial machines where the grooved disks or wheels are mounted to parallel shafts and where belts, timing chains or gears are used to rotate parts of the machine about parallel axes. The efficiency of the machine depends partly upon the alignment of the various rotating members. Use of a machine causes bearings to wear and can misalign other supports for the rotating parts. Such misalignment can lead to an accelerated wear and can cause a premature breakage of parts of the machine. Misalignment of rotating components of a sheave system also can degrade the quality of the products being produced by the machine. Additionally, breakage of machine parts leads to downtime of the machine and can impose a very substantial cost penalty on the manufacturing process. Accordingly, there is a demand for an apparatus to accurately assess sheave alignment. The above-described prior art laser apparatus is well suited to checking the alignment of components along a single rotational axis or for checking the position and alignment of parts relative to a reference plane. However, use of the prior art laser apparatus to check parallelism between a plurality of spaced apart rotational axes has been somewhat complicated. Typically, the job of checking machine alignment is assigned to the mechanic or technician who operates the machine. The typical technician may not have the time to perform a complicated sheave alignment check using the prior art laser apparatus. Instead, the technician may employ common xe2x80x9ceyeballxe2x80x9d methods of sheave alignment using a straight-edge. However, these xe2x80x9ceyeballxe2x80x9d methods don""t provide the necessary accuracy because these methods use the faces of the sheaves, which are rarely parallel to the grooves of the sheaves, as a reference.
Some prior art alignment procedures employ a height gage to check the height of one member relative to another. The prior art apparatus for checking the height of one member relative to another have included line levels and optical sight gages. The prior art laser apparatus also is well suited for this purpose. In particular, the prior art laser apparatus can be used to direct a beam from a first member or reference point to a second member. A target may be positioned on the second member, and the height of one member relative to the other can be determined by readings taken on the target. A target of this type often may be mounted on a target pole that enables the target to be moved vertically along the pole. The position of the target on the pole can be accurately determined mechanically or electromechanically. More accurate height information then can be achieved with the photosensitive target. This combination of a laser emitter, a photosensitive target and a target pole will yield very precise readings when the target pole is aligned perfectly vertically. However, the precision enabled by the combination of the laser emitter and photosensitive target can be offset if the target pole is not perfectly vertical. Accordingly, there is a demand for a laser alignment system with a height gage that compensates for misalignment of the target pole from a true vertical alignment
The subject invention relates to a target assembly for use with a laser, and particularly a laser capable of sweeping a flat optical plane. The target assembly comprises three light-sensitive target cells arranged in a triangle. The target cells may be mounted to a support and face substantially in a common direction relative to the support. The cell planes of two target cells may be coplanar, and the cell planes of all three target planes may be parallel. Preferably, the three targets are arranged to define a substantially equilateral triangle.
The support may include mounting means for mounting the target assembly to a sheave. Alternatively, the support may include mounting means for mounting the target assembly to a height gage. When used for sheave alignment, the support may include mounting structure for mounting the target assembly substantially vertically to a sheave or pulley wheel. When used with a height gage, the support can be mounted substantially horizontally and perpendicular to the target pole. In either embodiment, the mounting means of the support is formed for face-to-face engagement with the grooves of a sheave to allow genuine groove-to-groove alignment. The light-sensitive target cells may be two axis targets capable of generating X and Y coordinates for a laser beam impinging thereon. The target cells may be analog or digital, and in certain embodiments the light-sensitive target cells may be a CCD (charged coupling device).
The target assembly is used by first mounting the laser apparatus on a reference structure to which alignment of an adjustable member will be compared. For example, the reference may be one rotational sheave member in a sheave apparatus. The laser apparatus is leveled and trued by leveling mechanisms incorporated into the apparatus.
The target assembly then is mounted to a portion of the apparatus that is to be aligned. More particularly, the target assembly is mounted such that the support plate of the target assembly is approximately parallel to the optical plane that will be swept by the laser apparatus. Additionally, the target assembly is mounted such that all three light-sensitive target cells substantially face the laser, with one light-sensitive target cell being relatively close to the laser and with the two remaining light-sensitive target cells being spaced further from the laser.
The laser apparatus then is operated to sweep a flat optical plane, such that the laser impinges upon the respective target cells. Readings then are taken by the target cells to identify locations that are impinged upon by the laser. A difference in readings between the two target cells furthest from the laser apparatus will identify a pitch error between the plane of the three target cells and the laser scan plane. Similarly, a difference between the target cell closest to the laser and the average reading on the two more distant target cells (groove) will provide a yaw error reading.
In the typical sheave alignment operation, the support to which the light-sensitive target cells are mounted will be aligned substantially vertical on the sheave. However, the apparatus can be used with a height gage. When the target assembly is used with a height gage, the planar support to which the light-sensitive target cells are mounted will be substantially horizontal and at a selected elevational position on a target pole. Differences in readings of the respective targets can be used to precisely measure roll and pitch, and thereby to enable mathematical compensation for an alignment of the target pole other than perfectly vertical.